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Police use a variety of methods to determine if a person is driving after drinking or taking drugs. There are specific methods to test the level of alcohol or drugs in a person's system. There are also standardized tests to look for signs that someone is under the influence of drugs or alcohol.
There are devices that can detect the presence of alcohol or drugs in a drivers’ system. Police can also screen for possible drug or alcohol use by doing a field sobriety test.
The police can demand that a driver submit to roadside screening for alcohol and drugs. In most cases before doing this, the officer must have reasonable grounds to suspect that:
A driver who fails roadside screening can be arrested. Once arrested, they can be required to undergo testing for drugs or alcohol. The testing shows the specific amount of alcohol or drugs in the driver’s system.
Roadside alcohol screening involves having the driver blow into a breath device. It tells the police if the driver has alcohol in their system. The device will show a “pass”, “warn” or “fail” after the test is performed.
A breath sample in the "warn" range means that the sample was not over .08 blood alcohol concentration (BAC). However, it does indicate that it was over the provincial limit. This can lead to administrative penalties such as a roadside suspension.
A breath sample in the "fail" range indicates that it was over .08 BAC. In this case, the police will arrest you and require that you undergo further testing at the police station.
If the police have lawfully stopped your car, they can require you to blow into a roadside alcohol screening device. They can do this even if they do not have any grounds for believing you have consumed alcohol. They must have an approved screening device with them at the scene to do this.
Roadside drug screening is done by requiring the driver to provide a saliva sample. Like the roadside screening for alcohol, this test can determine if certain drugs, such as THC, are in the person’s system. It does not provide a measurement of the amount, however.
A standard field sobriety test (SFST) is another way to screen drivers for possible drug or alcohol use. The test typically includes checking a driver’s ability to:
After the roadside screening, the police can demand that the driver submit to testing. Before demanding this, they must have reasonable grounds to believe the driver is impaired to any degree by drugs or alcohol. This testing determines the amount of alcohol or drugs in the driver’s system. Multiple different tests can be done to confirm that a driver is impaired.
A variety of observations can lead to a police officer having reasonable grounds, such as:
Some of these factors may also be used in court to prove that a driver was impaired.
A common testing device that police use is the breathalyzer. Breathalyzer machines are calibrated to show the level of alcohol in the blood as a percentage. For example, a BAC of .04% means that you have 40 milligrams of alcohol in 100 milliliters of blood.
Another test that the police can use is a drug recognition expert evaluation. This evaluation is done by a trained officer. The evaluation includes:
An evaluation may show that the driver is impaired by drugs or a combination of alcohol and drugs. In this case, a bodily fluid sample is taken to confirm the findings of the evaluator. The bodily fluid may be blood, oral fluid or urine.
In some cases, the police may require a blood sample. They may do this:
If someone is impaired by both drugs and alcohol, a blood sample can show the levels of each.
It is a criminal offence to refuse to take any of the above tests or provide the required samples. The consequences for refusal are the same as being convicted of a criminal drug or alcohol driving charge. For more information, see Criminal Impaired Driving Offences.
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